Differential cooling in casting metals



July 18, 1950 P. P. ZEIGLER ETAL DIFFERENTIAL COOLING IN CASTING METALS2 Sheets-Sheet 1 Filed Dec. 26, 1947 INVENTORS P. ZE/GLER gLKYDE R.

PAUL

ST JOHN (5 July 18, 1950 P5P. ZEIGLER ET AL DIFFERENTIAL COOLING INCASTING METALS 2 Sheets-Sheet 2 INVENTORS PAUL P. ZE/GLEI? BQ LYDE R.37'- JOHN Filed Dec.

Patented July 18, 1950 DIFFERENTIAL COOLING IN CASTING METALS Paul P.Zeigler and Clyde R. St. John, Spokane,

Wash., assignors to Kaiser Aluminum & Chemical Corporation, acorporation of Delaware Application December 26, 1947, Serial No.793,997

7 Claims.

This invention relates to method for continuously casting metal ingots,billets and the like. More particularly, it relates to the continuouscasting of light metal ingots, billets and the like wherein the moltenmetal is solidified by application of a cooling fluid to the mold and/orto the ingot or billet in a particular manner as herein below described.

In the art of continuous casting of metals the general practice is toprovide an open-ended mold, which may be horizontal or vertical but, inthe case of large castings (such as rolling ingots and extrusionbillets), is preferably vertical; to feed molten metal continuously intoone end of the mold (the top end in the case of a vertical mold) andcontinuously withdraw solid casting from the opposite end of the mold;and to supply a cooling fluid continuously to the mold and/ or to thesolid casting as it emerges from the mold. The metal may or may not becompletely solidified in the mold; thus, the casting at the point whereit emerges from the mold may contain a core or crater of molten metal,which is solidified by cooling the casting below the mold. The coolinfluid may be a liquid, preferably water, or a gas, such as air. Coolingof the mold, and of the casting below the mold, may be accomplishedeither by the use of a cooling jacket, such as a water jacket, or bydelivering coolant directly to the mold or casting, as by means of spraypipes or a perforated tank. The casting procedure may be a strictlycontinuous process (in which the casting is cut to length withoutinterruption of the casting procedure) or it may be semi-continuous; i.e., a casting of desired length may be cast, the flow of metal stopped,the casting removed and the procedure commenced anew. Continuous"casting as herein used refers to either type of operation.

In the casting of relatively large castings, such as rolling ingots andextrusion billets, it is advantageous to use a liquid coolant, such aswater,

and to apply the coolant directly to the mold and to the casting belowthe mold; and, especially in the casting of large light metal ingots andbillets, such as aluminum and magnesium (including their alloys) ingotsand billets, it is advantageous to employ a short mold, with a low headof metal in the mold, and to complete solidification of the interior ofthe casting below the mold.

Whatever the method of cooling used, it has been the practiceheretofore, and regarded as essential, to cool the surfaces of the moldand the casting uniformly; that is, to cool each horizontal section (inthe case of a vertical casting operation) uniformly about the perimeterof that section. Typically, this is accomplished in the case of a systememploying a vertical mold and spraying water onto the sides of the moldand the casting from a perforated spray pipe or spraybox, by providingeach spray pipe or spray box surrounding the mold or casting withuniformly spaced holes of uniform shape and diameter.

The most advanced techniques of continuous casting have progressed to apoint where rapid casting of large ingots, billets and the like toproduce good quality castings is possible. Nevertheless, even with themost advanced techniques heretofore known a substantial amount ofrejected castings are produced owing to surface cracks, edge splits andbottom splits of the castings. These defects, when observed, lead torejection of the casting (i. e., it must be remelted and recast);otherwise, in rolling sheet, extruding or otherwise fabricating thecasting, a defective product may result. Even more serious, owing totheir latent nature, are internal ruptures of castings. These are notreadily observed, and castings having internal ruptures may be rolled,extruded or otherwise fabricated, and even put to their ultimate use,before detection of the defect.

It is an object of the present invention to provide an improved methodfor continuous casting of metals.

It is a further object of the invention to pro vide a method for castinglarge castings, particularly of light metals, by a continuous castingprocess which greatly diminishes defects in the castings.

It is a particular object of the invention to provide a method forcontinuously casting ingots, billets and the like, particularly of lightmetals, of large cross section and of square, rectangular or otherangular shape, while minimizing defects such as surface cracks, edgecracks, bottom splits and internal ruptures.

These and other objects of the invention will be apparent from theensuing description, the accompanying drawings and the appended claims.

We have discovered that defects in castings are substantially reduced inthe case of castings of square, rectangular or other angularcross-section, by employing a suitable continuous casting procedure andby causing substantially greater cooling of the surface of the moldand/or of the casting, at and near the angles or corners of the moldand/or casting than at points more widely spaced therefrom. And we havefurther discovered that a simple apparatus, employing spray pipes, aspray box or the like surrounding the mold or the casting, effectivelyaccomplishes the objects of the invention, it each pipe, spray box orthe like is provided with a. greater number or size of orifices fordelivery of coolant at and near these angles or corners than at pointsmore widely spaced therefrom.

For convenience, this cooling feature of the invention whereby certainareas of the mold and casting receive excess cooling. is hereinafterreferred to as differential cooling.

In the accompanying drawings several embodiments of the invention areshown. In these drawings;

Fig. 1 is a cross sectional view in elevation of a mold and ingotshowing a spray pipe cooling arrangement;

Fig. 2 is a cross sectional plan view taken along the line 2--2 of Fig.1, showing the mold and piping arrangement.

Fig. 3a is an enlarged .cross sectional view in elevation taken alongthe line 3-3 of Fig. 2.

Fig. 3b is a fragmentary elevational view of the pipes of Fig. 3a;

Figs. 4a and 4b are similar views taken along the lines 4-4 or |'4' ofFig. 2;

Fig. 5 is a plan view, "partly in cross section, of a second andpreferred embodiment of the invention showing a spray box type ofcooling mechanism;

Fig. 6 is a front elevation of a fiat pattern of the interior or workingsurface of the spray box of Fig. 5;

Fig. '7 is a cross sectional viewin elevation taken along the line ofFig. 5;

Fig. 7a is a cross sectional view in elevation taken along the line'|a'|q. of Fig. 5; and

Fig. 8 is a plan view of a third embodiment of the invention, showing asquare mold and spray box.

Referring now to Figs. 1 to 4b of the drawings, a roughly rectangular,vertical open-ended mold generally designated as l is supported frompouring platform 2 by any suitable means (not shown). Mold I hasrelatively short, rounded end portions 1a and relatively long, straightside portions lb. Within the mold and extending below it-is an embryoingot 3 comprising a pool of molten metal 4 and solidified casting 5,the pool 4 extending downwardly into and forming a, liquid core orcrater within the ingot. Surrounding and closely adjacent to the mold,is an upper spray pipe generally designated as 6 and surrounding andclosely adjacent to a lower portion of the mold adjacent the lower edgeof the same is a similar, lower spray pipe generally designated as 1.Spray pipe 6 has relatively short rounded end portions 60, andrelatively long, straight side portions 6b conforming generally to theconfiguration of mold I, and spray pipe 1 has similar end portions 1aand side portions 1b. Each spray pipe is provided with an inlet pipe 8.

Referring to Figs. 3a and 3b, illustrating the mid-sections of sideportions 6b of spray pipe 6, each mid-section is provided with a singlehorizontal row of circular orifices ll, of uniform diameter anduniformly spaced. The mid-sections of side portions 1b of spray pipe Iare similarly provided with circular orifices l2, which may be of thesame or different diameter and spacing as in spray pipe 6. As indicated,the angles of orifices H are 70 from the verti- The size, shape, spacingmay, however, vary from case to case, being selected in the light of thepressure of the coolant, its temperature and heat capacity and otherfactors well known in the art.

Referring, now to Figs. 4a and 4b, these views illustrate the orificedesign of spray pipes 6 and I at their end portions 60 and la,respectively, andalso at the end sections of each side portion 6b andlb. That is to say, considering Figs. 3a, 3b, 4a and 4b together, Figs.3a, and 3b show the orifice design at the mid-sections of side portionsof pipes 5 and while Figs. 4a and 4b show the orifice design at the endportions of these pipes and at the extremities of the side portionsadjacent the end portions,

Eachend portion 6a and the adjacent end sections of side portions 6b ofpipe 6 is provided with a double horizontal row of orifices II and Ila.Similarly, each end portion la andthe adjacent end sections of sideportions '|b is provided with a double row of horizontal orifices I2 and|2a. As indicated, each upper row of orifices is at an angle of 45 fromthe vertical and each lower row of orifices is also at an angle of 45from the vertical.

Referring now to Figs. 5 to 7. there is here shown a preferredembodiment of the invention involving a set or gang of three moldsinstead of a single mold and a spray box or chamber instead of spraypipes. Referring more particularly to Fig. 5, showing a plan view, agang of three molds 2| of roughly rectangular horizontal section, havingrounded end portions and straight side portions, are encased by a spraybox 22 provided with an inlet pipe or conduit 23 and having three wellsor openings 24 of the same shape as the molds and each being concentricwith its mold but of larger dimensions to allow an annular space betweenthe mold and the interior or working surface 25 of the spray box. Molds2| are supported by a suitable pouring platform (not shown).

Referring to Fig. 5, and to Fig. 6 showing in front elevation a fiatpattern of the interior surface 25 of the spray box 22, sections A1 andA2 of the interior surface 25 are disposed opposite the end portions andadjacent segments of the side portions of mold 2|, as shown more clearlyin Fig. 5. Similarly, sections B1 and B2 are disposed opposite themid-sections of the side portions of mold 2|. As shown in Figs. 6 and7a, an upper double row of relatively large orifices 3| and 3 aaredrilled in sections A1 and A2 opposite about the mid-portion of mold2| and a lower double row of relatively large orifices 32 and 32a aredrilled in sections A1 and A2 and opposit about the bottom portion ofmold 2 Upper an lower single rows of relatively small orifices 33 aredrilled in sections 31 and B2 opposite about the mid-portion and bottomportion, respectively, of mold 2|. As indicated, the upper rows oforifices 3| and 3|a are at an angle of 45 from the vertical and thelower rows of orifices 32 and 32a are also at an angle of 45 from thevertical. The upper rows of orifices 33 and the lower rows of orifices33 in sections B1 and B2 are at angles of 70 and 60 respectively fromthe vertical.

Referring now to Fig. 8, showing an embodiment of the invention adaptedto casting square ingots, there is shown in plan View an approximatelysquare mold 2|, having rounded corners; a spray box 22' provided with aninlet pipe or cal and of orifices l2, 60 from the vertical. 7 conduit 23and having a well or opening 24 and and angles of the orifices Y aninterior or working surface 25 defining said well and surrounding themold so as to leave an annular space between the interior surface andthe mold. Interior surface 25 is divided into corner areas A1, A1, A:and A4 adjacent the corners of the mold and casting, and intermediateareas B1, Ba, Ba and B4 adjacent the mid-sections of the mold walls andcasting walls. Larger orifices are drilled in corner areas A1, etc. thanin intermediate areas B1, etc., so as to supply a greater flow ofcoolant to the four corner sections of the mold and casting than tointermediate areas.

In operation, and referring to the embodiments of Figs. 1 to 4b, thecasting operation is commenced by means well known in the art. Thus, abottom portion (not shown), operated hydraulically, may be brought upagainst, and seal the bottom of mold 2. Water or other suitable cool antis caused to fiow through inlet pipes 8 into spray pipes 8 and l, thencethrough orifices H, Ha, l2 and 12a to the mold and to an area below themold. Molten metal may then be caused to flow from a melting furnace orholding vessel (not shown) through a trough and a suitable throttlingvalve (not shown) into mold i to fill it to a certain, predeterminedlevel. Then, while pouring continues, the aforementioned bottom piece iscontinuously lowered, the rate of pouring and lowering being socorrelated as to maintain the desired level of metal in the mold. As theingot emerges from the bottom of mold i, it is struck by coolant flowingthrough orifices i2 and 12a, the mold being meanwhile cooled by coolantfiowing through orifices I i and Ila, sufficiently to produce a solidshell or skin of metal about the ingot so that, below the mold, theingot serves as its own mold. The ingot or billet may be cut to lengthby suitable saw arrangement well known in the art, without interruptingthe casting procedure or, when an ingot or billet of desired length hasbeen cast, the pouring may be stopped and the solidified castingremoved.

The operation of the gang mold-spray box apparatus of Figs. 5 to 7a andof the square moldspray box of Fig. 8 are essentially the same exceptthat, in the gang mold apparatus, the three molds are operatedsimultaneously.

The several drawings illustrate the apparatus of the inventiondiagrammatically. In practice, to secure optimum results, a modicum oftrial and error will determine the optimum design; e. g., with referenceto Fig. 6, whether the lengths of sections A1 and A2, B1 and B2 of theinterior surface of the spray box, and whether orifices 3i, 3m, 32 and32a shall have 50, 100 or 150% greater area than orifices 33. Theparticular, optimum angle of the orifices may also vary from case tocase.

As shown by Fig. 8, square molds receive differential or excess coolingadjacent the corners only whereas, as shown by the preceding figures,rectangular molds having relatively long side portions and relativelyshort end portions receive differential cooling adjacent the corners andall along the end portions. As a general "working rule, where the moldpresents long and short sides, if the ratio of the long side to theshort side exceeds about 2 or 2 to 1, the short sides (or end portions)will receive differential cooling over their whole extent; but if thisratio is less than about 2 or 2 to 1, or the cross section approaches anequilateral polygon, only the corner sections will receive differentialcooling, as shown in Fig. 8.

With the foregoing general description and the following specificexamples, no difllculty beyond a modicum of trial and error will beencountered in designing the spray mechanism to achieve optimum results.

Further, the principle of the invention, 1. e., differential cooling,although preferably embodied in procedure and apparatus such as illus-.trated above, and used in conjunction with appurtenant apparatus suchas disclosed in Ennor, U. S. Patent No. 2,301,027, and Nicholls et al.,U. S. Patent No. 2,414,269, and applied to the casting of light metalssuch as aluminum, magnesium and their respective alloys, and employingwater as the coolant, is applicable to other procedures, apparatus,metals and coolants. Thus, the coolant may be other than water, e. g.,air, brine, oil or ethylene glycol. Also, the coolant may be enclosed ina jacket, as in Coats, U. S. Patent No. 1,503,479. Further, instead ofusing a greater orifice area adjacent the angles of the mold andcasting, other methods of differential cooling may be employed, e. g.,coolant may be supplied through the same orifice area but under greaterpressure, or colder coolant or a coolant having greater heat capacitymay be applied to the critical areas. Similarly, the mold wall may bemade thinner, or of more heat conductive material at these areas. Othermetals (including alloys of the same) which may be cast are copper,lead, zinc, and steel.

Following are specific illustrative examples of the invention.

Example 1 Mold and spray boa: design.--Each mold was constructed of asheet aluminum alloy (35), thick. It was of rectangular horizontal crosssection having straight, long sides and rounded ends. Depth (vertical)was 7", greatest length (horizontal) 32%," and width (horizontal) 10%;".Radius of curvature of the ends was 10%;". Three such molds were used.

The spray box was of the type illustrated in Figs. 5, 6 and 7, beingprovided with three wells to enclose the three molds. This spray box wasconstructed of sheet steel and was connected with a low pressure supplyof water to deliver water to the mold and casting at about 4 to 5 lbs.sq. in. The annular space between the interior surface of the box andthe mold was inch. Under these conditions, all the jets of water struckthe mold or ingot and ran down their sides without splashing.

The. orifice design will be best understood by reference to Figs. 5 and6 of the drawings. Each interior surface 25 defining a well 24containing a mold 2| was drilled to present four sections; that is, 'twoend sections A1 and A2 and two side sections B1 and B2. Each end sectionA1 or A: was disposed opposite and end portion of the mold and oppositeadjacent end segments of the sides of the mold. Each of these four endsegments covered by a section A1 or A: extended 3%" along a straightside of the mold, measuring from the point at which curvature of the endportion commenced.

In each of the end sections A1 and A2 were drilled an upper double rowof orifices 3i and 3i a adapted to deliver water to the mold aboutmidway between its top and bottom, and a lower double row of orifices 32and 32a adapted to deliver water to the ingot at the bottom of the mold.These orifices were centered 4 inches apart, the angle of upper orifices3|, 3ia being 45 and also of lower orifices 32, 32a being 45 from thevertical. Regarding A1 as the section lying nearer water inlet 23, theorifices in section A1 were of 95 diameter and the orifices of sectionA: were of is" diameter.

The two sections B1 and B2 disposed opposite the mid-sections of themold sides were each drilled with an upper single row of orifices andlower single row of orifices 33. The upper orifices were at angles of 70and centered inch apart, while the lower orifices were at angles of 60and centered inch apart, positioned to deliver water to the mid-portionsand bottom of the mold, respectively. All orifices were of 3," diameter.

Casting procedure-Metal poured was in some instances the well-knownaluminum alloy 248,

in others 758. Lowering rate of the casting was 2%" per minute.Temperature of the metal delivered to the mold was 1290 to 1320 F. inthe case of 24S, 1320 to 1340 F. in the case of 75S. Pouring wascommenced after the usual preparations had been made; e. g., after thepouring trough and valves had been brought to the proper temperature, asupply of water in the range of about 40-60 F. had been turned on andthe bottom of the mold was in place. When the metal in the mold reacheda level of about 4" above the bottom of the mold, lowering of the moldbottom was commenced and continued at the rate indicated. After astandard length of sheet ingot had been cast, (about 110"), pouringceased and the ingot was lowered out of the mold.

Example 2 x 39" ingots and 8" x 42" ingots were cast similarly, themolds and spray boxes being similar to that of Example 1 but designed toaccommodate the different size of ingot. Lowering rate in the case of10" x 39" ingots was 2%" per minute and, in the case of 8" x 42 ingots,it was 4 per minute.

In a variation of the previously described casting processes, it ispossible to continuously cast molten metal using only the top spraymeans, i. e., for example, spray pipe 6 as shown in Fig. 1.

By casting procedures as described in these examples and as generallyemployed in the art, and by the use of the differential coolingapparatus and method as described herein, it has been wherein moltenmetal is continuously supplied to an angular mold, the molten metal iscooled while in the mold at least sufficiently'to form a skin of olidmetal about the casting, and a casting having corners corresponding tothe angular shape of the mold is continuously withdrawn from the mold,the improvement which comprises cooling the metal substantially morerapidly at and near the corners formed by the mold than at points morewidely removed from the said corners.

2. The improvement of claim 1, wherein the metal isa light metal.

3. In the continuous casting of metals to .produce angular castings ofrelatively large crosssection, wherein molten metal is continuouslysupplied to the upper part of an angular. vertical mold, at least partlysolidified casting is continuously withdrawn from the bottom of themold, and liquid coolant is continuously sprayed onto the mold and ontothe casting below the mold, the improvement which comprises sprayingsubstantially more. coolant onto areas of the mold and the casting closeto and including the corners thereof than onto areas farther removedtherefrom.

4. A method of producing rectangular light metal ingots oi relativelylarge cross-section, which comprises continuously supplying the moltenmetal to the upper .part of a'n'open-ended vertical mold ofapproximately rectangular horizontal cross section and having a maximumhorizontal length at least twice the width of the mold, continuouslyspraying liquid coolant onto the sides and end portions of the mold andthe sides and end portion of the ingot below the mold, and somaintaining an excess supply of coolant to the end portions of the moldand casting and to adjacent portions of the sides of the mold and ingotlying close to the end portions as to substantially reduce cracking ofthe ingot.

5. The method of claim 4, wherein said light metal is predominantlycomposed of aluminum. 6. A method of producing rectangular light metalingots of relatively large cross-section, which comprises continuouslysupplying the molten metal to the upper part of an open-ended verticalmold of rectangular horizontal cross section and having horizontaldimensions such that no one such dimension exceeds any other by a factorof more than two, continuously spraying liquid coolant onto the sides ofthe mold and of the ingot below the mold, and so maintaining an excesssupply of coolant to the corner sections of the mold and ingot as tosubstantially reduce cracking of the ingot.

7. The method of claim 6, wherein said light metal is predominantlycomposed of aluminum.

PAUL P. ZEIGLER. CLYDE R. ST. JOHN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,074,812 Sendzimer Mar. 23, 19372,127,515 Hazelett Aug. 23, 1938 2,301,027 Ennor Nov. 3, 1942 2,304,258Junghan Dec. 8, 1942 2,310,893 Brenner Feb. 9, 1943 2,414,269 NichollsJan. 14, 1947 FOREIGN PATENTS Number Country Date 884,498 France Apr.27, 1943

